I haven't noticed a spool holder on here specifically for the Dibond version of the Mendel 90, so I made one. It's based strongly on fest's version for the acrylic panel machine.
I haven't tried it with more than one spool but I can't imagine it would be a problem.
As always, I'd love to see yours if you print them.
I used ABS with 25% infill for mine and they seem fine so far.
The metal bar in the picture is a 450mm length of 10mm diameter aluminium extrusion but you can use any 10mm diameter rod. The hole in the bracket is actually 11mm in the stl but it comes out a bit tight so a 10mm rod fits well.
It doesn't need screwing to the machine, just a push fit. You will need to print with support to generate the part which sits over the Mendel90 frame.